Structural study of the aggregates formed by the dinucleoside phosphate G2 in aqueous solution

Abstract

X-ray diffraction results in magnetically oriented samples of aqueous solutions of the sodium salt of the dinucleoside phosphate G2 in the cholesteric N∗ phase are presented. The symmetry of the diffraction confirms a model of stacking of tetrameric disks forming cylindrical aggregates in the N∗ phase. A weak band at 7 Å not previously observed gives further information on the inner structure of the cylindrical aggregates. Analysis of the diffraction peak position in low angle evidences a change in functional behaviour of the distance α between cylinder axes as a function of the volume concentration c_v of G2. In the H phase, a α c_v ^−1/2 as it should for infinite cylinders; in the N∗ phase, a α c_v ^−1/3, typical of finite cylinders. The cross-over of functional behaviour occurs at the N∗[sbnd]H phase transition. There is therefore cylinder growth along the N∗ phase.